1. Field of the Invention
This invention relates generally to oil and gas well cementing compositions and methods and specifically to an additive package which achieves a highly dispersed, low fluid loss cement composition during placement thereof.
2. Description of the Prior Art
Cement compositions are used in the oil and gas industry to cement the annular space in the well bore between the surrounding formation and the pipe or casing. Typically the cement slurry is pumped down the inside of the casing and back up the outside of the casing through the annular space. The amount of water which is used in forming the cement slurry will vary depending upon the type of hydraulic cement selected and the job conditions at hand. The amount of water used can vary over a wide range, depending upon such factors as the required consistency of the slurry and upon the strength requirement for a particular job. Many times, the hydraulic cement must be placed within or next to a porous medium, for example earthen strata in the well bore. When this happens, water tends to filter out the of slurry and into the strata during placement and setting of the cement. Many difficulties are related to an uncontrolled fluid loss of this type, such as an uncontrolled setting rate, improper placement of the slurry, impaired strength properties, and a contamination of the surrounding strata. These conditions are all undesirable in oil and gas well cementing operations.
In order to lessen the fluid loss from the aqueous cement slurry, various materials have been employed in the past. Known fluid loss additives utilized in cement compositions include cellulosic materials, polysaccharides, polyacrylamides, polyvinyl alcohol, polymethacrylates, polyamines, and polyvinylpyrrolidone. Known cellulosic fluid loss materials include, for example, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, carboxymethylhydroxyethylcellulose, natural starches and mixtures thereof. The polyamine materials include the polyalkylenepolyamines, polyalkylenimines, and mixtures thereof.
Various ethoxylates have also been used in the past in cementing slurries, mainly to reduce air entrainment. See, for example, U.S. Pat. No. 4,351,671, to Rosenberg et al., issued Sep. 28, 1982, in which an ethoxylated nonylphenol is added to a cement slurry containing a lignin type water reducing agent to reduce air entrainment.
U.S. Pat. No. 4,209,336, to Previte, issued June 24, 1980, teaches the addition of non-ionic surface active condensation products of octylphenol or nonylphenol with ethylene oxide as compressive strength enhancing additives for hydraulic cement compositions.
U.S. Pat. No. 4,398,958 teaches the use of a non-ionic surfactant such as an ethoxylated primary or secondary alcohol or a nonylphenol-ethylene oxide condensate additive to ensure proper distribution of expanded polystyrene beads in a lightweight concrete.
We have discovered that the addition of selected ethoxylates surprisingly and unexpectedly improves the fluid loss and dispersant qualities of oil and gas well cementing slurries while maintaining favorable suspension properties. Specifically, the ethoxylates included in the additive package of the invention decrease the viscosity of certain cement slurries while also decreasing fluid loss.